In Colorado and other areas of the United States are located what are popularly known as "oil shales" occasionally exposed at the surface of the ground but generally overlaid by overburden to varying depths. Oil in the form of kerogen is entrapped within the shale deposits. For many years efforts have been made to recover the oil, and several processes have been proposed for the purpose. Many proposals have involved first the mining of the shale and then the surface extraction of the oil from the mined shale. The mining techniques and associated extraction techniques have generally involved intolerably high capital investments, energy expenditures, ecological damage, and extraction and refining costs.
The present commercial techniques for extracting bitumen from the bituminous sands of northern Alberta involve strip-mining the sands, conveying the minded sand to surface processing plants, and separating the bitumen from the sand. In one commercial operation, a substantial amount of hot water containing waste contaminants requires to be disposed in a tailings pond. The conventional processing is thus seen to require relatively expensive mining techniques which become increasingly unsuitable as the amount of overburden over the bituminous sand formations increases in depth, and is also seen to involve severe environmental impact in that the strip-mining per se seriously damages the surface and in that the waste liquid ponds further contaminate the surface environment. Furthermore, the bituminous sands underlying the surface plants and facilities and tailings disposal areas and rendered inaccessible for mining.